Our laboratory has been studying a murine PEX2 null animal model for the human peroxisomal biogenesis disorder Zellweger syndrome. We have determined that peroxisomal dysfunction in vivo affects neuronal proliferation, migration, survival and differentiation during CNS development. However, the contributions from intrinsic CNS defects versus extrinsic systemic organ dysfunctions and the role of peroxisomal lipid deficiencies or specific peroxisomal pathway defects have not been determined. We propose an integrated series of in vitro and in vivo approaches to address the following questions: Specific Aim #1. Are the defects in neuronal migration and differentiation in PEX2 -/- mice caused by factors intrinsic or extrinsic to the CNS? What is the role of peroxisomal lipid deficiencies or specific defects in peroxisomal B-oxidation or plasmalogen pathways in causing these abnormalities? We will directly visualize the dynamics of migrating neurons from control and PEX2 -/-mice by videomicroscopy using cerebral and cerebellar slice cultures and cerebellar neuron-glial cultures. The in vitro differentiation of control and PEX2 mutant cerebellar Purkinje cells and granule neurons will be examined. We will determine the effect of correcting deficiencies for plasmalogens or docosahexaenolc acid on the cellular defects in PEX2 neurons. We will compare the CNS defects observed in PEX2 -/- mice with those seen in mice with peroxisomal defects limited to plasmalogen and/or B-oxidation pathways (MFE2 -/-, MFE2/MFE1 -/-, PEX7 -/-) using these assays for neuronal migration and differentiation. We will evaluate the role of CNS intrinsic versus systemic peroxisomal dysfunction in the pathogenesis of CNS defects by both in vitro and in vivo transfection methods to restore PEX2 function in selected CNS cell types or brain regions. Alternatively, we will use in vivo transplantation of normal or peroxisome-defective neuronal progenitors into normal or mutant developing cerebral cortex or cerebellum. Specific Aim #2: Do hepatic factors contribute to the CNS defects in peroxisome defective mice? We will evaluate how CNS development is altered when bile acid deficiency is corrected in vivo in PEX2 -/-mice. We will determine whether bile acid products accumulate in the brain of PEX2 / mice. We will examine whether toxic substances from the PEX2 mutant liver cause CNS dysfunction by determining the effect of adding exogenous bile acid intermediates or hepatocyte conditioned medium on the in vitro neuronal defects in control, PEX2 -/, plasmalogen or B-oxidation defective mice. Specific Aim #3: What is the role for peroxisomes in developing cerebellar Purkinje cells and/or granule neurons? Conditional deletion of the PEX2 gene in cerebellar Purkinje cells and/or granule neurons will determine the role of peroxisomes for the development of these neurons in the absence of systemic organ peroxisome deficiency.